1. Field of the Invention
The present invention relates to a turbine rotor which is configured by welding separate component parts of the turbine rotor, and more particularly to a turbine rotor of which component parts are made of suitable heat-resisting alloy and heat-resisting steel, and a steam turbine provided with the turbine rotor.
2. Description of the Related Art
Energy saving of the thermal power plant including a steam turbine is being performed vigorously after the energy crisis, and technology for suppression of the emission of CO2 is being watched with interest in view of the global environmental protection in these years. As part of it, needs for a highly efficient plant are increasing.
To increase power generation efficiency of the steam turbine, it is very effective to raise the steam temperature to a high level, and the recent thermal power plant having the steam turbine has its steam temperature raised to 600° C., or more. There is a tendency in the world that the steam temperature of the turbine will be increased to 650° C., and further to 700° C. in future.
The turbine rotor supporting moving blades which are rotated by receiving high-temperature steam has a high temperature because the high-temperature steam flows to circulate around the turbine rotor. Besides, a high stress is generated in the turbine rotor by the rotations of the turbine rotor. Therefore, the turbine rotor must withstand a high temperature and a high stress. Such a turbine rotor may have portions, which have a particularly high temperature, configured of an Ni-base alloy having high strength even at a high temperature. In a case where the Ni-base alloy is used, its manufacturable upper size is limited and the Ni-base alloy costs high, so that it is desirable that the Ni-base alloy is used for only portions which must be made of the Ni-base alloy, and other portions are made of an iron-steel material.
Under the circumstances described above, recently, there has been disclosed a technology to produce a turbine rotor by combining the Ni-base alloy and the iron-steel material. In a case where the turbine rotor is produced by connecting the Ni-base alloy and the iron-steel material by welding or the like, it is general to select the connecting iron-steel material of a type resistant to a high temperature in order to make a size of the portion made of the Ni-base alloy as small as possible. Specifically, a technology is disclosed in, for example, JP-A 2004-36469 (KOKAI) that the turbine rotor of a steam turbine into which steam having a high temperature of 675° C. to 700° C. flows is configured by coupling the Ni-base alloy and 12Cr steel. JP-A 2000-64805 (KOKAI) discloses a technology that the turbine rotor of a steam turbine is configured by coupling 12Cr steel and CrMoV steel.
As described above, the temperatures of main steam and reheated steam have a tendency to become higher in order to obtain high power generation efficiency. And, in a case where the individual portions of the turbine are made of the same material as those of a related art in order to realize a steam turbine in which a steam temperature exceeds 650° C., the steam turbine cannot withstand the high-temperature steam. Accordingly, it is effective to use the Ni-base alloy having high heat resistance for the portion of the steam turbine which has a high temperature.
But, the above-described conventional method for producing the turbine rotor by combining the Ni-base alloy and the 12Cr steel has a drawback that a large thermal stress is generated in the connected portion because a coefficient of linear expansion of the Ni-base alloy is largely different from that of the 12Cr steel.